Currently, display systems use either non-processor based display adapters such as VGA (Video Graphics Arrays) which contain only low-level logic functions and registers and require that the host processor application software or operating system environment perform essentially all of the display generation and manipulation of graphics processor based adaptors such as TIGA (Texas Instruments General Architecture) based boards which interface via a high-level language or command list system. Further details of arrangements of the latter type are to be found in "Texas Instruments Graphics Architecture User's Guide", 1989; "TMS34010 User's Guide", August 1988; and "TIGA340 Interface" all of which documents are currently available to the public from Texas Instruments Incorporated. Reference may also be made to U.S. Pat. No. 4,752,893.
In the past, and indeed until fairly recently, only the `dumb` register based display adapters were available. Although some firmware was available to interface these adapters via software calls (the BIOS extensions), such firmware was too slow and cumbersome to be used for advanced high performance applications. This limitation resulted in most application programs accessing directly to the registers and frame buffer of the display hardware.
Upon the advent of higher performance hardware, either at the host processor (CPU) level or at the display adapter level it became possible to rethink the standard display interface, and higher level display environments such as Microsoft Windows.RTM. started to appear. This was further encouraged by the need for effective multitasking where several application programs need to interface to the user at the same time but with total independence from each other.
Unfortunately, to fully take advantage of these display environments application programs had to be written especially for them--or at least an interface `driver` be generated which performed the link. In addition, the old application was used to having the entire machine, including the display adapter all to itself; something which is, of course, not possible in a multitasking environment.
Existing application software was therefore a priori incompatible with the new graphics environment trends.
Some compromise was offered by emulating the hardware model of the old logic adapter through a combination of software and the existing hardware. This, although providing a small consolation was not entirely satisfactory since the poor performance of such a system, again using Microsoft Windows as an example, limits its use to text mode displays only. The more useful graphics modes are not displayable in a window and the user must revert to full screen single task operation. Any software using EGA (Enhanced Graphics Arrays) or VGA graphics is therefore incompatible with multitasking multi-window systems which require that all display accesses are handled by the host processor software. If an `old application` is executed which requires unique control of the display system, then currently the displays from the multi-window manager are suspended and the `old-application` takes control of the full screen display thereby removing the advantages of a multi-window user environment.
An aim of the invention is to overcome these drawbacks.